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<pre><code><span class="macro">macro_rules!</span> <span class="macro declaration">println</span> <span class="punctuation">{</span>
    <span class="punctuation">(</span><span class="punctuation">$</span><span class="punctuation">(</span><span class="punctuation">$</span>arg<span class="punctuation">:</span>tt<span class="punctuation">)</span><span class="punctuation">*</span><span class="punctuation">)</span> <span class="operator">=</span><span class="punctuation">&gt;</span> <span class="punctuation">(</span><span class="punctuation">{</span>
        <span class="punctuation">$</span>crate<span class="punctuation">:</span><span class="punctuation">:</span>io<span class="punctuation">:</span><span class="punctuation">:</span>_print<span class="punctuation">(</span><span class="punctuation">$</span>crate<span class="punctuation">:</span><span class="punctuation">:</span>format_args_nl<span class="punctuation">!</span><span class="punctuation">(</span><span class="punctuation">$</span><span class="punctuation">(</span><span class="punctuation">$</span>arg<span class="punctuation">)</span><span class="punctuation">*</span><span class="punctuation">)</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="punctuation">}</span><span class="punctuation">)</span>
<span class="punctuation">}</span>
#[rustc_builtin_macro]
<span class="macro">macro_rules!</span> <span class="macro declaration">format_args_nl</span> <span class="punctuation">{</span>
    <span class="punctuation">(</span><span class="punctuation">$</span>fmt<span class="punctuation">:</span>expr<span class="punctuation">)</span> <span class="operator">=</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span><span class="punctuation">{</span> <span class="comment">/* compiler built-in */</span> <span class="punctuation">}</span><span class="punctuation">}</span><span class="punctuation">;</span>
    <span class="punctuation">(</span><span class="punctuation">$</span>fmt<span class="punctuation">:</span>expr<span class="punctuation">,</span> <span class="punctuation">$</span><span class="punctuation">(</span><span class="punctuation">$</span>args<span class="punctuation">:</span>tt<span class="punctuation">)</span><span class="punctuation">*</span><span class="punctuation">)</span> <span class="operator">=</span><span class="punctuation">&gt;</span> <span class="punctuation">{</span><span class="punctuation">{</span> <span class="comment">/* compiler built-in */</span> <span class="punctuation">}</span><span class="punctuation">}</span><span class="punctuation">;</span>
<span class="punctuation">}</span>

<span class="keyword">fn</span> <span class="function declaration">main</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span>
    <span class="comment">// from https://doc.rust-lang.org/std/fmt/index.html</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello"</span><span class="punctuation">)</span><span class="punctuation">;</span>                 <span class="comment">// =&gt; "Hello"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello, </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"world"</span><span class="punctuation">)</span><span class="punctuation">;</span>   <span class="comment">// =&gt; "Hello, world!"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"The number is </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="numeric_literal">1</span><span class="punctuation">)</span><span class="punctuation">;</span>   <span class="comment">// =&gt; "The number is 1"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">?</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="punctuation">(</span><span class="numeric_literal">3</span><span class="punctuation">,</span> <span class="numeric_literal">4</span><span class="punctuation">)</span><span class="punctuation">)</span><span class="punctuation">;</span>          <span class="comment">// =&gt; "(3, 4)"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">value</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> value<span class="operator">=</span><span class="numeric_literal">4</span><span class="punctuation">)</span><span class="punctuation">;</span>      <span class="comment">// =&gt; "4"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="numeric_literal">1</span><span class="punctuation">,</span> <span class="numeric_literal">2</span><span class="punctuation">)</span><span class="punctuation">;</span>           <span class="comment">// =&gt; "1 2"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="numeric_literal">4</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="numeric_literal">42</span><span class="punctuation">)</span><span class="punctuation">;</span>             <span class="comment">// =&gt; "0042" with leading zerosV</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="numeric_literal">0</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="numeric_literal">1</span><span class="punctuation">,</span> <span class="numeric_literal">2</span><span class="punctuation">)</span><span class="punctuation">;</span>   <span class="comment">// =&gt; "2 1 1 2"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">argument</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> argument <span class="operator">=</span> <span class="string_literal">"test"</span><span class="punctuation">)</span><span class="punctuation">;</span>   <span class="comment">// =&gt; "test"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="numeric_literal">1</span><span class="punctuation">,</span> name <span class="operator">=</span> <span class="numeric_literal">2</span><span class="punctuation">)</span><span class="punctuation">;</span>          <span class="comment">// =&gt; "2 1"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">a</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="variable">c</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="variable">b</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> a<span class="operator">=</span><span class="string_literal">"a"</span><span class="punctuation">,</span> b<span class="operator">=</span><span class="char_literal">'b'</span><span class="punctuation">,</span> c<span class="operator">=</span><span class="numeric_literal">3</span><span class="punctuation">)</span><span class="punctuation">;</span>  <span class="comment">// =&gt; "a 3 b"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"{{</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">}}"</span><span class="punctuation">,</span> <span class="numeric_literal">2</span><span class="punctuation">)</span><span class="punctuation">;</span>                       <span class="comment">// =&gt; "{2}"</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">1</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="variable">width</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">,</span> width <span class="operator">=</span> <span class="numeric_literal">5</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">&lt;</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">-</span><span class="format_specifier">&lt;</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">^</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">&gt;</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">+</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">#</span><span class="variable">x</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="numeric_literal">27</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="numeric_literal">0</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="punctuation">-</span><span class="numeric_literal">5</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">#</span><span class="numeric_literal">0</span><span class="numeric_literal">10</span><span class="variable">x</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="numeric_literal">27</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">0</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="numeric_literal">5</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">,</span> <span class="numeric_literal">0.01</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">1</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">2</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="numeric_literal">0</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">,</span> <span class="numeric_literal">0.01</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="numeric_literal">0</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">2</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="numeric_literal">1</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">,</span> <span class="numeric_literal">0.01</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span>    <span class="string_literal">"x"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">,</span> <span class="numeric_literal">0.01</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="numeric_literal">2</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span>   <span class="string_literal">"x"</span><span class="punctuation">,</span> <span class="numeric_literal">5</span><span class="punctuation">,</span> <span class="numeric_literal">0.01</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> is </span><span class="format_specifier">{</span><span class="variable">number</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="variable">prec</span><span class="format_specifier">$</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> <span class="string_literal">"x"</span><span class="punctuation">,</span> prec <span class="operator">=</span> <span class="numeric_literal">5</span><span class="punctuation">,</span> number <span class="operator">=</span> <span class="numeric_literal">0.01</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">, `</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">` has 3 fractional digits"</span><span class="punctuation">,</span> <span class="string_literal">"Hello"</span><span class="punctuation">,</span> <span class="numeric_literal">3</span><span class="punctuation">,</span> name<span class="operator">=</span><span class="numeric_literal">1234.56</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">, `</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">:</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">` has 3 characters"</span><span class="punctuation">,</span> <span class="string_literal">"Hello"</span><span class="punctuation">,</span> <span class="numeric_literal">3</span><span class="punctuation">,</span> name<span class="operator">=</span><span class="string_literal">"1234.56"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">, `</span><span class="format_specifier">{</span><span class="variable">name</span><span class="format_specifier">:</span><span class="format_specifier">&gt;</span><span class="numeric_literal">8</span><span class="format_specifier">.</span><span class="format_specifier">*</span><span class="format_specifier">}</span><span class="string_literal">` has 3 right-aligned characters"</span><span class="punctuation">,</span> <span class="string_literal">"Hello"</span><span class="punctuation">,</span> <span class="numeric_literal">3</span><span class="punctuation">,</span> name<span class="operator">=</span><span class="string_literal">"1234.56"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello {{}}"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"{{ Hello"</span><span class="punctuation">)</span><span class="punctuation">;</span>

    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">r"Hello, </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal">!"</span><span class="punctuation">,</span> <span class="string_literal">"world"</span><span class="punctuation">)</span><span class="punctuation">;</span>

    <span class="comment">// escape sequences</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"Hello</span><span class="escape_sequence">\n</span><span class="string_literal">World"</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="escape_sequence">\u{48}</span><span class="escape_sequence">\x65</span><span class="escape_sequence">\x6C</span><span class="escape_sequence">\x6C</span><span class="escape_sequence">\x6F</span><span class="string_literal"> World"</span><span class="punctuation">)</span><span class="punctuation">;</span>

    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="escape_sequence">\x41</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> A <span class="operator">=</span> <span class="numeric_literal">92</span><span class="punctuation">)</span><span class="punctuation">;</span>
    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="variable">ничоси</span><span class="format_specifier">}</span><span class="string_literal">"</span><span class="punctuation">,</span> ничоси <span class="operator">=</span> <span class="numeric_literal">92</span><span class="punctuation">)</span><span class="punctuation">;</span>

    <span class="macro">println!</span><span class="punctuation">(</span><span class="string_literal">"</span><span class="format_specifier">{</span><span class="format_specifier">:</span><span class="variable">x</span><span class="format_specifier">?</span><span class="format_specifier">}</span><span class="string_literal"> </span><span class="format_specifier">{</span><span class="format_specifier">}</span><span class="string_literal"> "</span><span class="punctuation">,</span> thingy<span class="punctuation">,</span> n2<span class="punctuation">)</span><span class="punctuation">;</span>
<span class="punctuation">}</span></code></pre>